1. Field of the Invention
The present invention relates to a film formation method and film formation apparatus for forming a metal film such as a copper film used as an interconnection of a semiconductor, and also relates to a storage medium.
2. Description of the Related Art
Recently, to meet the requirements for a high operating speed of a semiconductor device, a high degree of micropatterning of an interconnection pattern, and a high degree of integration, demands have arisen for decreasing the capacitance between interconnections, increasing the conductivity of an interconnection, and increasing the electromigration resistance. As a technique meeting these demands, a Cu multilayered interconnection technique using copper (Cu) having conductivity and an electromigration resistance higher than those of aluminum (Al) and tungsten (W) as an interconnection material and using a low-k film as an interlayer dielectric film is attracting attention.
As methods of forming a Cu film of a Cu multilayered interconnection, a physical vapor deposition (PVD) method such as sputtering, a plating method, and a chemical vapor deposition (MOCVD) method that uses a metal organic material by vaporizing it are known. However, the PVD method has a low step coverage, and this makes it difficult to bury a film in a fine pattern. In the plating method, a Cu film contains large amounts of impurities because the plating solution contains additives. Although the MOCVD method readily achieves a high step coverage, large amounts of impurities such as carbon (C), oxygen (O), and fluorine (F) from side-chain groups oriented in Cu atoms remain in a Cu film, and this makes the film quality difficult to improve. In addition, the material is very expensive because the side-chain groups oriented in Cu atoms are complicated. Also, a source gas is difficult to stably supply because the process is thermally unstable and the vapor pressure is low.
By contrast, Patent Document 1 listed later has disclosed a technique in which a CuCl plate is placed in a chamber and etched by generating an Ar gas plasma to produce desorbed species of CuCl, dissociation species of Cu and Cl are produced from the desorbed species by using the Ar gas plasma, and a Cu film is formed on a substrate by direct reduction by making the temperature of the substrate lower than that of the CuCl plate. Patent Document 1 describes that this technique makes it possible to increase the film formation rate, use inexpensive materials, and form a Cu film containing no residual impurities.
Unfortunately, it is difficult for the technique of Patent Document 1 to completely remove Cl from the Cu film, so a slight amount of Cl may remain. Even if the residual amount of Cl is slight, corrosion of a Cu interconnection poses problems such as the rise in interconnection resistance and deterioration of the reliability. Also, since the substrate surface is exposed to the plasma in the initial stages of film formation, the substrate may be chemically or physically damaged. In particular, a low-k film used as an interconnection easily raises the dielectric constant or breaks a microstructure when exposed to the plasma (plasma damage). Furthermore, the plasma sputters members other than the CuCl plate in a reactor, so these members are damaged, or sputtered particles make impurities remain in a film or cause contamination. Accordingly, application of the technique of Patent Document 1 to the Cu multilayered interconnection requires expensive mechanisms and materials in order to solve the above problems.
On the other hand, as a method other than the semiconductor fabrication process, Patent Document 2 listed later has disclosed a method of fabricating a Cu interconnection by a method that is not a wet plating method by using an inexpensive material. This method forms a thin Cu film by coating a substrate with copper(II) formate (Cu(OCHO)2) as an inexpensive organic Cu compound or its hydrate, and heating the substrate in a non oxidizing ambient. Similarly, Non-Patent Document 1 listed later has reported that a Cu interconnection is formed by heating a substrate coated with copper(II) formate dihydrate with a laser beam having a narrowed light diameter. Each of these methods uses the phenomenon that copper(II) formate changes into Cu by thermal decomposition. Although these methods can form a Cu film at a low cost, they are unsuited to bury a metal in a fine shape processed to a nanometer level such as an interconnection of an ultra large scale integrated circuit (ULSI), and the electrical conductivity is lower than the original value of Cu.
Non-Patent Document 2 listed later has reported an attempt that uses inexpensive copper(II) formate hydrate as the material of MOCVD. A powder of copper(II) formate hydrate is placed in a material vessel, and a carrier gas is supplied while the material is heated. A vaporized component produced by heating is transported through a pipe by a carrier gas to the surface of a substrate heated in another reactor. The transported vaporized component thermally decomposes on the substrate surface to form a Cu film on it.
Non-Patent Document 3 listed later has revealed that this vaporized component produced in the material vessel is copper(I) formate. Copper(I) formate (Cu(OCHO)) that readily vaporizes is produced as a gas from copper(II) formate that hardly vaporizes in accordance with a reaction formula indicated by2Cu(OCHO)2→2Cu(OCHO)+CO+CO2+H2O  (1)and this gas is transported to a substrate.
Since copper(I) formate is a material that very easily thermally decomposes as reported in Non-Patent Document 3, a thin Cu film is readily formed at a low temperature from copper(I) formate in accordance with a reaction formula indicated by2Cu(OCHO)→2Cu+2CO2+H2  (2)
In this method, a formate group (OCHO) as a ligand is readily thermally decomposed into CO2 or H2 and exhausted and hence is hardly entrapped in a Cu film. This facilitates the formation of a high purity Cu film containing no impurity. However, a method in which a carrier gas carries a material vaporized from a solid material is generally largely affected by the thermal conduction state in a solid material vessel at a low pressure, and this makes stable supply of the vaporized material difficult. Also, copper(II) formate as the material thermally decomposes and forms a Cu film in the solid material vessel. That is, deterioration of the material readily occurs.
Furthermore, Non-Patent Document 3 has reported silver as a metal that reacts similarly to copper as a formate, and a silver film can be formed as an interconnection layer by the same method, but the same problems as when copper is used similarly arise.
Patent Document 1: Jpn. Pat. Appln. KOKAI Publication No. 2004-27352
Patent Document 2: Japanese Patent No. 2745677
Non-Patent Document 1: A. Gupta and R. Jagannathan, Applied Physics Letters, 51(26), p 2254, (1987)
Non-Patent Document 2: M.-J. Mouche et al, Thin Solid Films 262, p 1, (1995)
Non-Patent Document 3: A. Keller and F. Korosy, Nature, 162, p 580, (1948)